Nb-Al合金高温氧化机理

通过自编软件建立了铝氧化膜与基体铌界面的原子集团模型,用递归法计算了合金的原子埋置能、原子结合能等电子参数,从电子层面分析铌合金高温氧化机理.研究表明:铝通过晶界扩散偏聚在合金表面,并与氧结合生成致密的Al2O3氧化膜,阻挡氧向铌基体扩散.晶界和稀土元素能提高氧化膜与基体间的原子结合能,增加其界面的结合强度,加强氧化膜与基体铌间的黏附性.因此,通过在合金中添加稀土元素或细化合金晶粒均能提高铌合金的抗高温氧化性能.

High temperature oxidation mechanism of Nb-Al alloys

The formation mechanism of the oxide film on Fe-Cr-Al alloy, the effects of sulfur on the adhesion of the oxide film, and the role of RE element Y on the improvement of the oxide film adhesion were systematically studied on an electronic level, so that the physical nature of oxidation of the alloy was revealed. The results show that Al atom (compared with Cr or Fe atom ) has the lowest environment-sensitive embedding energy when O atoms are present on the alloy surface, thus leading to an outward diffusion of Al atoms from the interior of the alloy, and hence to the segregation of Al atoms on the alloy surface. Oxygen atoms are easy to combine with Al atoms to form Al₂O₃ oxide films on the alloy surface due to its high affinity with Al atoms. The impurity S has a lower environment-sensitive embedding energy on the interface between the Al₂O₃ oxide film and the alloy matrix than within the alloy matrix, suggesting that S can diffuse (segregate) to the interface. S atoms segregated on the interface weakens the cohesion of Al₂O₃ oxide film with the alloy matrix. Y is easy to combine with sulfur to form a stable sulfide within the interior of the alloy matrix, which inhibits the diffusion of sulfur to the Al₂O₃ oxide film /matrix interface. Y added into the alloy can thus markedly increase the adhesion of the oxide film with the alloy matrix, and significantly improve the high-temperature oxidation resistance of the alloy.